1. Field of the Invention
The present invention relates to a bump printing apparatus, and more particularly, to a bump printing apparatus that can increase the printability of solder bumps being printed on a printed circuit board.
2. Description of the Related Art
In general, flip chip bonding, tape automated bonding and wire bonding are being used to interconnect external boards, such as printed circuit boards (PCBs) or wafer level packages (WLPs), to chips.
Among them, flip chip bonding has been widely used to manufacture portable electronic products since this method increases the number of pads per unit area.
According to flip chip bonding, solder bumps are formed on a wafer in order to appropriately bond chips and external circuitry. Particularly, a technique for manufacturing solder bumps has been developed to form solder bumps having appropriate conductivity, uniform lengths and fine pitches.
According to this solder bump forming technique for flip chip bonding, the characteristics of solder bumps and an application range thereof are determined according to the materials used to form solder bumps. Examples of the solder bump forming technique may include a soldering method of contacting pad electrodes to solder, a screen printing method of forming solder bumps on pad electrodes by screen printing and reflowing the solder bumps, a solder ball reflow method of mounting solder balls onto pad electrodes and reflowing the mounted solder balls, and a plating method of performing solder plating on pad electrodes.
Among them, a screen printing method has been widely used to form solder bumps in that the process of forming solder bumps in this manner is simple, manufacturing costs are low, and bumps of desired metallic material can be formed.
Solder bumps are printed according to this screen printing method by which, while a (metal) mask having holes arranged into a predetermined pattern makes close contact with a printed circuit board, a solder paste is compressed and moved across the upper surface of the mask to thereby fill the holes.
However, according to the current screen printing method, since the mask is merely placed onto and makes close contact with the upper surface of the printed circuit board, gaps may be generated between the board and the mask.
These gaps mostly occur around the edges of the board in surface contact with the mask, where printing defects, such as the spreading of the solder paste, short circuits and missing bumps, in which bumps are not formed, occur in large quantities.
As a result, the printability of the solder bumps is reduced to thereby cause a deterioration in product quality and a reduction in the reliability of a circuit board.